Liquid-crystal display devices using liquid crystal compositions are widely utilized in displays such as clocks, electronic calculators, mobile phones, personal computers, televisions and so forth. These liquid-crystal display devices utilize refractive index anisotropy, dielectric anisotropy or the like of liquid crystal compounds. As an operating mode in the liquid-crystal display device, twisted nematic (TN), super twisted nematic (STN), bistable twisted nematic (BTN), electrically controlled birefringence (ECB), optically compensated bend (OCB), in-plane switching (IPS), vertical alignment (VA) and so on that perform display mainly using one or more polarizers have been known. Further, a mode that exhibits electric birefringence by applying an electric field in an optically isotropic liquid crystal phase has also been studied in recent years (Patent Literatures 1 to 13 and Non-patent Literatures 1 to 3).
Further, a wavelength variable filter, a wavefront control element, a liquid crystal lens, an aberration correction element, an aperture control element, an optical head device and so forth using the electric birefringence in a blue phase as one of the optically isotropic liquid crystal phases have been proposed (Patent Literatures 10 to 12).
A classification based on the driving mode of the element includes the passive matrix (PM) type and the active matrix (AM) type. The PM type is classified into the static type, the multiplex type and so on. The AM type is classified into the thin-film transistor (TFT) type, the metal insulator metal (MIM) type and so on according to the type of switching elements.
As the liquid crystal composition used in the LCD device, examples of optically isotropic liquid crystal compositions that contain a compound having two biphenylene groups and a difluoromethoxy linking group, or a tetracyclic compound having a dioxane ring are reported in Patent Literatures 14 to 24. These compounds have large dielectric anisotropy, and have an effect of reducing a driving voltage when used in a display device such as a display or the like.
However, in the mode that exhibits electric birefringence by applying an electric field in an optically isotropic liquid crystal phase, when a liquid crystal composition using the compound having a large dielectric anisotropy is used for reducing the driving voltage, the permittivity of the liquid crystal composition tends to increase.
For example, in a display mode using a polymer stabilized blue phase (PSBP) as a polymer/liquid-crystal composite material, when a polymer/liquid-crystal composite material having large permittivity is used in an optical device, the time for injecting charges into the thin film transistor (TFT) is increased, and problems such as increase in driving voltage, reduction in transmittance and so forth occur.
To solve such problems, a polymer/liquid-crystal composite material characterized by a low driving voltage and a low permittivity is demanded.